Problem: Balance this nuclear reaction by supplying the missing nucleus. 249/98 Cf+ + _____ → 263/108 Sg + 4 1/0 n

We’re being asked to complete the nuclide symbols for the particles that are required to balance the following nuclear reaction:

${}_{\mathbf{98}}{}^{\mathbf{249}}\mathbf{Cf}\mathbf{ }\mathbf{+}\mathbf{?}\mathbf{ }\mathbf{\to }\mathbf{ }{}_{\mathbf{108}}{}^{\mathbf{263}}\mathbf{Sg}\mathbf{ }\mathbf{+}\mathbf{ }\mathbf{4}\mathbf{ }{}_{\mathbf{0}}{}^{\mathbf{1}}\mathbf{n}$

Heavy (large atomic mass) elements undergo radioactive reactions  (nuclear reactions) in order to increase the stability of their nuclei. 

Nuclear fusion is a nuclear reaction in which two or more atomic nuclei combine to form one or more larger atomic nuclei and subatomic particles.

The element in the reaction can be represented as: